1. Debug your application and look at the exception. You might need to look at the InnerException or Response property (on TwitterQueryException) for more info. This might indicate what the problem could be.

2. Find a similar example in the downloadable source code, LinqToTwitterDemo project to see if it has the same problem.

3. Write a small sample application that reproduces the same error.

4. Open Fiddler or Firebug and look at the response from Twitter.

5. If those options don't help you solve the problem, you can post the sample app, stack trace, and Fiddler response here.

1. Move the auth.IsAuthorized logic out of the query where you can see it's value before the query occurs. This might tell you whether the problem only occurs during public or friend queries.

2. Materialize the query before assigning it to datasource.

3. Catch the exception when the query materializes. Then drill down into the Exception/InnerException object/s and look at the Response property of the TwitterQueryException, which holds the message from Twitter.

4. You're interested in finding the Response from Twitter and maybe even the HTTP error.